Lithium ion batteries have, over the past couple of decades, been used in portable electronic equipment and more recently in hybrid and electric vehicles. Initially, lithium ion batteries first employed lithium cobalt oxide cathodes. Due to expense, toxicological issues and limited energy capacity, other cathode materials have, or are being developed.
Other lithium metal oxides (LMOs) have been or are being developed comprising Ni or Mn. Desirable lithium metal oxides that have been developed generally are complex metal oxides that contain a combination of Ni, Mn and Co. These also may contain dopants or coatings that improve one or more properties such as cycle life. The lithium metal oxide may be stoichiometric or essentially stoichiometric such as those described by U.S. Pat. Nos. 6,964,828; 6,168,887; 5,858,324; 6,368,749; 5,393,622 and European Pat. Publ. Nos. EP1295851, EP0918041, and EP0944125 and Japanese Patent Disclosure No. 11-307094. Likewise, the lithium metal oxide may be made with an excess of lithium such as those described by U.S. Pat. Nos. 6,660,432 and 6,677,082 and Japanese Appl. No. H8-37007.
These lithium metal oxides have been made by solid state synthesis where particulate precursors are mixed or milled and then heated to a temperature to form the LMO. Examples of this method are described in U.S. Pat. No. 6,368,749 and EP0944125, EP1296391 and EP1193782. The lithium metal oxides have also been formed by first precipitating a complex precursor in continuously stirred reactors with the complex precursor compound subsequently heated with a lithium compound to a temperature to form the LMO. Examples of these methods are described by U.S. Pat. No. 6,964,828 and Japanese Patent Disclosure No. 11-307094. Other methods have also been described such as hydrothermal methods and sol gel methods to form the complex oxides. Examples of these are described in U.S. Pat. No. 7,482,382 and EP0813256.
Generally, LMOs have tended to be made from complex metal compounds, “LMO precursors,” precipitated from a continuously stirred reactor that are then mixed with lithium containing compounds and heated sufficiently to form the LMOs. They have generally been made this way to avoid the problems encountered with simple mixing or milling of precursors such as non-uniformity of the chemistry, primary grain/particle size and secondary particle size. Unfortunately, continuous stirred reactors require long reaction residence times to achieve desired secondary particle size, varying reaction conditions that preclude them from being used continuously (e.g., secondary particle size growth over time) and large capital investment due to large tanks necessary to make the LMOs on a production scale.
Accordingly, it would be desirable to provide an improved method to make LMOs that avoids one or more problems of the prior art. In particular, it would be desirable to provide a method that allows for continuous or semi-continuous operation, short residence times, small capital cost and ease of controlling secondary particle size and distribution as well as desired primary particle/grain size.